We propose to investigate several iron proteins identified in bacterial oxygenase systems and in yeast mitochondria. In these proteins the iron is either directly involved in catalysis or it is active in charge transfer, or both. We will use Fe57-Mossbauer spectroscopy as our main tool. Mossbauer spectra reveal, via electric and magnetic hyperfine interactions, the ground state levels of the iron 3d electrons. Comparison of the electronic structure observed for different states in the reaction cycle will allow us to monitor microscopic changes taking place at the active center. Such information can help to unravel the reaction mechanism. Specifically, we will study the following enzymes: Cytochrome c oxidase from S. cerevisiae (Bakers' yeast), the terminal enzyme of the mitochondrial electron transport chain. The spectra of the two heme a groups will be quantitatively evaluated. This technique will provide imformation that cannot be obtained in any other way. By combining Mossbauer and EPR results obtained on the same sample the electron flow within c oxidase can be partitioned. Non-heme dioxygenases cleave aromatic rings by oxygen insertion reactions. We propose to study a variety of extra- and intradiol cleaving enzymes with Mossbauer spectroscopy. The studies proposed here are a part of a cooperative effort involving five research groups at the Universities of Minnesota and Wisconsin. Cytochrome c' from R. Rubrum, a heme protein with an unusual electronic configuration.